Structural basis for the inhibition of voltage-dependent K⁺ channel by gating modifier toxin

Voltage-dependent K⁺ (K_v) channels play crucial roles in nerve and muscle action potentials. Voltagesensing domains (VSDs) of K_v channels sense changes in the transmembrane potential, regulating the K⁺-permeability across the membrane. Gating modifier toxins, which have been used for the functional analyses of K_v channels, inhibit K_v channels by binding to VSD. However, the structural basis for the inhibition remains elusive. Here, fluorescence and NMR analyses of the interaction between VSD derived from K_vAP channel and its gating modifier toxin, VSTx1, indicate that VSTx1 recognizes VSD under depolarized condition. We identified the VSD-binding residues of VSTx1 and their proximal residues of VSD by the cross-saturation (CS) and amino acid selective CS experiments, which enabled to build a docking model of the complex. These results provide structural basis for the specific binding and inhibition of K_v channels by gating modifier toxins.